Traditionally grain storage tanks unload from the top, exposing workmen to the risk of falling into the tank and suffocating. Also, unloading from the top meant that the last material in was the first out, and uniform discharge of the encased material by succeeding layers was very difficult. Gravity flow discharge is not new in the context of railway hopper cars; and a patent has dealt with gate valves for material storage containers on train hoppers or the like (i.e., U.S. Pat. No. 3,556,479), wherein traditional slide gates were discarded in favor of a wedge or pyramid shaped valve operatively connected to the top of the container. While such a gate valve provided novel features of operation of the valve from above, utilization of the weight of the container's contents to seal the valve, protection of the valve mechanism from the elements and relatively even flow of the contained material, either hydraulic means or a threadable shaft and hand wheel arrangement were contemplated as constituting the drive means to raise the valve against the weight of the contained material, thereby permitting the container to empty. Further, a wedge or pyramid shaped valve connected to a threadable shaft or a hydraulic opening means required an additional valve member attached to the bottom of the container to engage the valve in order to prevent it from rotating while material flowed out. Thus, an axially asymmetrical valve added complexity to the container and its discharge means.